Six different laboratory pain-inducing methods will be compared and evaluated for their sensitivity to the analgesic effects o a variety of drugs in order to developan objective, standard and valid pain "thermometer" or battery for human analgesic assays. Three pain response parameters, pain threshold, pain tolerance and pain sensitivity range, will be correlated within and between techniques and pain response parameters and a correlation matrix created, which will be subjected to factor analysis in order to validate the existence of a specific pain factor, termed "pain endurance" previously observed. It is hoped that such a pain factor will greatly assist in the development of a short but valid pain "thermometer". For the drugs, both crossover (complete and incomplete) and single-dose designs will be compared. Aspirin, codeine, morphine, narcotic antagonists, etc., will be evaluated with the new pain "thermometer". Paid, healthy, adult volunteers will be used double-blind conditions. The potential pain-inducing and contrasting anesthetic properties of various osmolarities of sodium chloride will be investigated with our standard deep somatic (intramuscular) saline methods. The latter will be modified to permit its practical application for human analgesic assays. Furthermore, work with this deep somatic approach may allow the development of an experimental pain model and possibly lead to a better understanding of pain, both clinical and in the laboratory.